This invention generally relates to catheters and methods of preventing occlusion and infection of catheters, such as intravascular catheters and other body cavity catheters. More specifically, but not exclusively, this invention relates to infusing a lock solution into an indwelling catheter, such as, for example, an indwelling intravascular catheter, for inhibiting occlusion and infection in an animal having an indwelling catheter.
By way of background, catheters are used with increasing frequency to treat patients requiring a variety of medical procedures. Catheters offer many advantages for patients; for example, catheters provide ready access to a patient's vasculature without repeated injections for infusion of fluids such as drugs, nutrients, electrolytes or fluids used in chemotherapy, or for the removal of blood on an intermittent basis. In hyperalimentation treatment, catheters are usually used for infusion of large volumes of fluids. In chemotherapy, catheters are used for infusion of drugs on an intermittent basis, ranging from daily to weekly. For hemodialysis, dual-lumen catheters are typically used—usually three times per week—to remove blood from the patient's circulatory system for treatment and to return treated blood back to the patient. One lumen allows removal of blood, while the other lumen allows blood to return.
Catheters are also used to perform other functions and to convey fluids into and out of other body cavities besides veins, as noted above. For example, catheters are placed into arteries to measure blood pressure or remove arterial blood for analysis of gases reflecting lung function; catheters are placed into the peritoneum (the space surrounded by the peritoneal membrane and external to organs in the abdomen) to perform peritoneal dialysis and remove fluids and toxins from the patient; and other catheters are placed into the fluid around the nervous system (cerebral spinal fluid) for removal of this fluid or administration of drugs, and into the subcutaneous space for administration of various drugs or fluids. Such catheters are also subject to infection and to other problems addressed herein.
Catheters can either be acute, or temporary, for short-term use or chronic for long-term treatment. Catheters used to access a patient's bloodstream are commonly inserted into central veins (such as the vena cava) from peripheral vein sites. Another alternative is placement of a dual-lumen chronic central venous dialysis catheter (a “CVDC”) through the internal jugular vein. Adequate hemodialysis requires removal and return of 250-400 mL of blood per minute.
Catheters, especially chronic venous catheters, have drawbacks. The use of both temporary and chronic CVDCs is associated with certain complications that may require catheter removal, catheter replacement and/or administration of medical therapies. They can become occluded by a thrombus, and even if extreme care is taken, the catheters can increase a patient's risk of infection.
Considering first the problem of infection, great care must be taken in the placement and use of a chronic catheter to prevent infection of the patient at the site of access or within the vascular system. The foreign surfaces of catheters can create smooth surfaces at which bacteria can grow, and at which white cells are unable to surround or “phagocytize” the bacteria. One way that a catheter, particularly a chronic catheter such as a CVDC, can give rise to infection is by the migration of bacteria around the catheter across the protective dermal layers. To address this problem, a chronic CVDC usually includes a DACRON cuff attached to the catheter and placed under the skin, which promotes ingrowth of fibrous tissue, fixes the catheter in position, and prevents bacterial migration around the catheter. Most chronic CVDCs in use in the U.S. today have single subcutaneous Dacron® cuffs, placed in the tunnel, 1-4 cm beneath the skin exit site. For dual lumen catheters such as the Ash Split Cath™ and Bard Hickman® catheters, there is one cuff on the catheter. For single-lumen catheters such as Tesio® catheters, there is a single Dacron cuff for each catheter. Cuffed, tunneled CVDCs have a decrease in the rate of exit site infection and catheter-related bloodstream infection (“CRBSI”) versus uncuffed catheters, but these infections still occur. It is believed that the only chronic CVDC in the U.S. at present that does not have a subcutaneous Dacron cuff is the Schon™ catheter. In this catheter a subcutaneous plastic clip connects two Tesio catheters. This clip fixes the catheters in position and apparently prevents pericatheter bacterial migration in a manner similar to a Dacron cuff. Chronic CVDCs are typically made from one of three types of materials: silicone, polyurethane, or polyurethane derivatives.
For chronic CVDC the most common cause of catheter infection is contamination of the connector hub, and the predominant route of contamination is endoluminal. Catheters, particularly venous catheters, are frequently accessed with syringes, or uncapped and directly connected to IV lines, creating a situation wherein the probability of microbial infection is relatively high. The major determinant of the rate of infection is the frequency with which the catheter hub is opened and the major preventive step is the care in disinfection of the hub and prevention of contamination of the hub. Since endoluminal contamination is the major cause of CRBSI in chronic CVDC, the determinants of infection center on the procedures and handling of the catheter.
Several studies have indicated a rate of bloodstream infection during use of chronic CVDC of 1.1 to 2.2 per 1,000 patient days. One study demonstrated a catheter-related bacteremia rate of 2.2 to 3.8 bacteremic episodes per 1,000 patient days, the lower rate being for catheters placed surgically rather than radiologically. Another study of new tunneled catheters reported that 19% of catheters became infected in a mean of 62 days after catheter placement, representing a rate of 3 infections per 1,000 days. This means that each patient has approximately a 10% chance of developing bloodstream infection during each month. There is no evidence that the rate of CRBSI increases with duration of use of a chronic CVDC. In fact, practical experience and various studies have shown that the rate of CRBSI is the same over the many months of use. Tests indicate that the risk of CRBSI is the same for each period of time that the patient has a catheter. Over time the patient has a higher chance for infection merely because there is more time at risk for infection. The longer the patients have a chronic CVDC, the greater the chance that an infection will occur, but this is merely due to greater time for a constant risk of exposure.
CRBSI in dialysis patients is usually associated with modest symptoms and clears after antibiotic therapy. However, in some patients, signs of infection are much more severe and include all of the symptoms of Systemic Inflammatory Response Syndrome (“SIRS”) (tachycardia, tachypnea, abnormal temperature and white count) plus hypotension. Often these patients must be hospitalized and given intravenous antibiotics. In spite of this care, patients often remain seriously ill until the infected catheter is removed. Studies have shown that CRBSI in hemodialysis patients is caused most frequently by Staphylococcus species such as S. Epidermidis. However, hemodialysis patients are reported to have a greater proportion of CRBSIs due to S. Aureus than do other patient populations and a significant number of infections are due to gram-negative organisms.
The mortality rate following CRBSI in ICU patients has been reported to be 3-25%. It was reported in a recent year that about 60,000 of the 300,000 patients on dialysis in the U.S. had chronic CVDC. Assuming an average incidence of CRBSI of only 21,000 patient-days at risk, about 120 of these patients would be expected to develop CRBSI each day. At the lowest reported mortality rate of 3%, 3-4 ESRD patients die from CRBSI each day. At the highest reported mortality of 25%, 30 ESRD patients die from CRBSI each day. Furthermore, the cost attributable to caring for a single CRBSI episode in hospitalized patients has been reported to be between $3,700 and $29,000. Costs may be higher for patients with CRBSI related to chronic CVDC, given the higher cost of removing and replacing a chronic CVDC. Given the serious consequences of CRBSI, the acute illness of the patient who apparently has bacteremia, and the frequent decision to remove the catheter on the presumption that it is the source, there is a great need for alternative means for fighting catheter infection.
Turning now to the problem of catheter occlusion, intraluminal thrombus formation can significantly impair catheter flow, as can thrombus formation just outside the tip of the catheter. Impairment of the flow may lead to catheter removal or administration of drugs such as tPA to resolve these thromboses. In order to prevent clotting of catheters in blood vessels between uses of a CVDC, catheters have commonly been filled with a lock solution that comprises a concentrated solution of the commonly used anticoagulant, heparin (usually up to 10,000 units of heparin per catheter lumen). The heparin lock solution is injected into each lumen immediately after each use, and typically left in the catheter until the catheter is accessed again. The heparin lock solution is then withdrawn from the catheter before the next use because infusing this amount of heparin into a patient's bloodstream runs the risk of causing excessive bleeding. During the catheter lock procedure the injected volume of solution is preferably exactly the same as the internal volume of the catheter. Even when this volume is injected exactly, however, about ⅓ of the injected anticoagulant volume typically leaves the end of the catheter, causing some systemic anticoagulation of the patient in the hours after a dialysis procedure.
Even with the use of a heparin lock solution, the catheter can become occluded between uses from coagulation of blood in the catheter. Blood may be found in the catheter because, for example, an inadequate volume of heparin was originally infused within the catheter lumen, the heparin diffused or convected from the lumen, or residual blood remains in the lumen during the catheter lock. This often results in formation of a thrombus with concomitant loss of flow through the lumen. The occluded catheters frequently must be removed and/or replaced.
Furthermore, it has been reported that thrombi and fibrin deposits on catheters may serve as a nidus for microbial colonization of the intravascular devices, and that catheter thrombosis might therefore be one factor associated with infection of long-term catheters. Thus, the use of anticoagulants or thrombolytic agents may have a role in the prevention of catheter-related bloodstream infections. However, recent in vitro studies suggest that the growth of coagulase-negative Staphylococci on catheters may also be enhanced in the presence of heparin. In addition, the routine use of heparin to maintain catheter patency, even at doses as low as 250 to 500 units per day, has caused some patients with anti-heparin antibodies to experience heparin-induced thrombocytopenia (HIT Syndrome). This serious syndrome can result in severe and sudden thromboembolic and hemorrhagic complications.
Heparin solutions have no proven intrinsic antiseptic properties to prevent infection after catheter hub contamination. The lack of antiseptic properties of a 5000 U/mL heparin lock was confirmed by a study performed by BEC Laboratories, Inc. under the standard USP antimicrobial effectiveness test protocol. “Antiseptic”, as used herein, means “relating to the prevention of infection by inhibiting the growth of infectious agents”, as defined in Stedman's medical dictionary. Heparin, in fact, may help to promote growth of bacteria within the “biofilm” layer of protein on the catheter surfaces (protamine has the opposite effect). The “biofilm” proteins on the catheter surfaces can protect bacteria from antibiotics and white cells. Also, heparin induces the loss of platelets and, paradoxically, can induce clotting in some patients (the “white clot” syndrome).
In order to achieve a catheter lock solution that is resistant to clotting and resistant to microbial infection, some have proposed the inclusion of antibiotics in heparin lock solutions or prophylactic systemic delivery of antibiotics to patients with CVDCs. However, because of frequent hospitalizations and receipt of antibiotics to treat bloodstream and vascular access infections, hemodialysis patients are at high risk for infection with drug-resistant bacteria. The rapid increase in vancomycin-resistant enterococci (VRE) in the United States has been attributed to use of antimicrobials, especially empirically prescribed vancomycin. Vancomycin is used commonly in dialysis patients for empiric therapy of symptoms of bloodstream infection because it can be administered once a week and is effective against two common pathogens, coagulase-negative Staphylococci and Staphylococcus Aureus. The greater the use of vancomycin, however, the greater the risk of inducing vancomycin-resistant staphylococcus, and if this is the cause of septicemia, there are then no effective drugs with which to treat these patients. Use of prophylactic vancomycin and other antibiotics to prevent catheter infection is therefore discouraged, and alternate means for fighting catheter infection are greatly needed.
Significant resources are currently being invested in a search for alternatives to heparin for catheter lock that do not have the above disadvantages, and for catheter formulations that have antimicrobial properties without including antibodies. For example, the present inventor has previously described catheter lock solutions including antimicrobial concentrations of citrate. Citrate provides effective anticoagulant properties when used in a catheter lock solution and, at a high concentration (i.e., at about 47% by weight), citrate also provides effective antimicrobial properties. One challenge presented by such a solution is that the high specific gravity of a concentrated citrate solution makes the solution tend to “run out” of a catheter over time. In addition, there are potential serious side effects if highly concentrated citrate is infused into a patient's bloodstream. These problems can be reduced by lowering the concentration of citrate in the solution, and even low concentrations of citrate have been shown to be at least equal to heparin in terms of maintaining catheter patency; however, lowering the concentration of citrate does result in a decrease in antimicrobial effects.
In light of the above-described problems, there is a continuing need for advancements in the field of catheter lock solutions. The present invention addresses this need and provides a wide variety of benefits and advantages.